Diffusion furnace

ABSTRACT

A DIFFUSION FURNACE STRUCTURE HAVING A CABINET WHICH SUPPORTS STACKED MODULES, EACH OF WHICH INCLUDES A DRAWER TRAY CARRYING AN ELONGATED CAPSULE ENCLOSING A HEATING ELEMENT, THE ELEMENT BEING ELECTRICALLY CONNECTED TO THE FURNACE CONTROLS SUCH THAT THE ELEMENT CAN BE QUICKLY DISCONNECTED FROM THE CABINET WHEN THE TRAY IS OPENED, AND A PLURALITY OF METAL LEAVES CONSTITUTING A   PART OF THE ELECTRICAL CONNECTORS FOR A HEATING ELEMENT, AND WHICH ARE BENDABLE TO FACILITATE AXIAL REMOVAL OF THE ELEMENT THROUGH THE OPENING IN EITHER OF THE ENDS OF AN ELONGATED DIFFUSION FURNACE CAPSULE OR THE LIKE.

Fbb.l6,1971 K A-LANG [26.21065` DIFFUSION FURNACE 2 Sheets-Sheet lOriginal Filed April l2. 1965 16, K A LANG Re.

DIFFUSION FURNACE Original Filed April 12. 1965 2 Sheets-Sheet f n w \,vN N l 5 Y WM k t\ United States Patent Y 27,065 DIFFUSION FURNACE KarlA. Lang, 93 Rivo Alto Canal, Long Beach, Calif. 90803 Original No.3,361,863, dated Jan. 2, 1968, Ser. No. 447,343, Apr. 12, 1965.Application for reissue Dec. 23, 1969, Ser. No. 887,782

Int. Cl. H05b 3/66 ILS. Cl. 13-25 17 'Claims Matter enclosed in heavybrackets appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT 0F THE DISCLOSURE A diffusion furnace structure having acabinet which supports stacked modules, each of which includes a drawertray carrying an elongated capsule enclosing a heating element, theelement being electrically connected to the furnace controls such thatthe element can be quickly disconnected from the cabinet when the trayis opened; and a plurality of metal leaves constituting a part of theelectrical conectors for a heating element, and which are bendable tofacilitate axial removal of the element through the opening in either ofthe ends of an elongated diffusion furnace capsule or the like.

This invention relates lto furnace structures, and more particularly toimprovments in diffusion furnaces.

More specifically, this invention relates to the type of furnace whichutilizes an elongated heating coi] surrounded by a tube of refractorymaterial. In this type of furnace, thick metal straps are welded to theends of the coil for connection to a `current source. Additionally, thecoil is tapped by welding additional straps `to selected turnsintermedi-ate its ends. Such additional straps are also adapted to besupplied with heating currents from the source to permit the interior ofthat portion of the coil intermediate the tapped connections to beselectively raised to a higher temperature than that which would beobtained by currents applied through the end connections alone.

Typically, such furnaces are operated with a hollow quartz tube insertedin the heating coil and extending the length thereof. One end of thequartz tube is capped, and materials to be heated in the furnace, suchas semiconductor materials and the like, are inserted into the open endof the quartz tube.

In such furnaces as heretofore known, all of the metal straps are ledthrough one end of the furnace, where connections are made to the sourceof current. Thus, the strap at one end of the furnace is a short elementextending through the adjacent end ofthe furnace, whereas the strap atthe opposite end is a member which extends the length of the coil to theend of the furnace where the connections are made to the source.Similarly, the straps for the tapped connections are of differentlengths. The reason for this arrangement is to facilitate the removal ofthe heating coil from one end of the furnace when it is necessary forsuch coil to lbe replaced.

In this latter connection, the ends of the straps extending out of thefurnace are bent outwardly to permit them to be secured to terminalblocks to which connections from the current source are made. The strapsthemselves are of relatively large stock, being of the order of aneighth of an inch thick and up to an inch wide, which necessitates theirbeing preformed with the bends in them before they are welded to theheating coil. Accordingly, if these straps were led out of the oppositeends of the furnace, they could not be bent straight to permit theheating coil to 'be removed from either end of the furnace.

In addition to the foregoing, such prior art furnaces do not lendthemselves to ready replacement of heating elements in certainenvironments, such as so-called clean rooms, in which it is essential toeliminate all possible dirt from the surrounding air. Such furnaces arebuilt in large, heavy supporting structures, and are expensive. Since aheating element cannot be removed from a furnace without releasingparticles of refractory material in the surrounding air, its replacementin such surroundings cannot be tolerated. Rather, it is necessaryto'remove the entire furnace support structure from the area in order tomake the necessary change, and bring it back in after the change ismade.

Such operations involve considerable la-bor and exlpense, and keep thefurnace out of commission for an undesirably long period of time.Frequently, in order to keep a production line going, a complete furnaceand suport structure must be installed in place of the one beingserviced.

It is an object of my invention to provide an improved furnace structurewhich overcomes the above and other disadvantages of the prior art.

Another object of my invention is to provide a diffusion furnace inwhich strap connections to different points on the heating coil can beled out of the ends of the furnace nearest their connections, and stillpermit the heating coil to be removed from either end of the furnace.

A further object of my invention is to provide an improved furnacestructure in the form of a portable cartridge unit containing theheating coil, and which can readily be removed from a supportingstructure and carried out of a work area when it is necessary to replacethe heating element.

Yet another object of my invention is to provide a furnace structure inwhich individual portable 'furnace units of light weight can be arrangedin a stack, but wherein each is separately and easily removable from thestack to permit it to be replaced with a similar unit.

It is also an object of my invention to provide `a unique diffusionfurnace, comprising a minimum number of component parts of simple designand rugged construction.

The above and other objects and advantages of my invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings of an illustrative embodiment thereof, in which:

FIGURE 1 is a perspective view of a furnace structure in which a pair ofreplaceable cartridge heating assemblies are arranged in a stack on abase cabinet structure which houses controls for the heating elementsinthe heating assemblies, each heating assembly being located in arespective cabinet module, with one of the modules having its frontpanel removed and the cartridge therein moved to the exterior by meansof the drawer mechanism on which it is carried;

FIGURE 2 is a fragmentary sectional view taken along the line 2 2 ofFIGURE 1, showing the internal constructions for the cartridge units;

FIGURE 3 is an end view of the tube of refractory material in which theheating coil is mounted;

FIGURE 4 is an enlarged side elevation view of the heating coil with themetal straps welded thereto extending in opposite directions past theends of the coil, and showing the plurality of metal leaves welded tothe ends of the straps for connection to exterior terminal blocks;

FIGURE 5 is an exploded view of the elements of a terminal block;

FIGURE 6 is an enlarged sectional view of one of the terminal blocksmounted over a slot in the end of the cartridge housing, showing moreclearly the manner in which the metal leaves welded to one of the strapconnections to the heating coil are directed through the slot in thehousing and secured to the terminal block; and

FIGURE 7 is a sectional view taken along the line 7 7 of FIGURE 6,showing .the portions of the metal strap and the metal leaves wheret-hey are welded together.

Referring to FIGURE l, the furnace structure 10 is formed of a basecabinet 11 on top of which is support- :d a stack of pairs of cabinetmodules 12, 13 which support individual cartridge heating assemblies.The modules l2, 13 are identical in construction, each being providedwith a front panel, as indicated at 14 for the module 13, which canreadily be attached to and removed from the front of the module. Withineach module is a cartridge heating assembly 15 which has an elongatedhousing 16 that sets in a drawer tray 17. The tray 17 is adapted to bepulled out a suficient distance to permit the housing 16 to `be lifted'out of the tray for servicing ind/or replacement. As indicated, the tray17 is provided with side bars 18 slidably mounted in channels 19 whichare secured to the sides of the module 12. The bars 18 may be adapted toglide on suitable bearings Within the :hannel 19 in the manner employedin conventional drawer :onstructions for ling cabinets and the like.

Each cartridge assembly 15 is a complete furnace unit. Referring toFIGURE 2, the housing 16 is formed of a cylindrical tube 20 having endcaps 21, 22 having aligned central openings 23, 24. Extending throughthe :enter of lthe housing is a tube of refractory material within whichis an elongated heating coil 26. Preferably :he tube 25 is formed Iwithan interior groove to nestably eceive the outer portions of the turns ofthe coils, Where- Jy the internal rib, indicated at 27, extends betweenthe :urns of the coil.

Referring to FIGURE 3 along with FIGURE 2, the efractory tube 25 isformed of two semicylindrical sec- ;ons 28, 29. `In assembly, thesections 28, 29 are placed around the heating coil 26, as by laying thecoil in one section with its turns nested in the grooves of thatsecyion, and then placing the other section over the exposed aortion ofthe coil with the turns of the coil located in :he grooves of thatsection.

Preparatory to assembling the coil 26 in the refrac- :ory tube 25 (seeFIGURES 2-4), metal straps are velded to the coil. In this connection, apair of relatively short metal straps 31, 32, of the order of four orlive nches in length, are Welded to the end turns of the coil Z6.Additionalstraps 33, 34 which are several inches long- :r than the endstraps are welded to respective turns of :he coil a few inches from eachthereof. As shown, the nner ends of the straps 33, 34 are bent inwardly,where- Jy the main bodies of the straps are spaced from the coil. ['hesections 28, 29 of the refractory tube 25 are formed vith notches 36, 37in the confronting edge portions `hereof to form slots for the bent endsof the straps 33, i4. The bottoni surfaces of these straps thus rest onthe Juter surface of the refractory tube 25.

'This type of heating unit is one which is adapted to leat the interiorof the coil 26 to extremely high temperitures, e.g., of the order of2,500 F. whichrequires that he coil be formed of relatively thick stock,e.g., wire )f the order of a quarter of an inch in diameter, and netalstraps for connection to a` current source of upvards to an inch inwidth and an eighth of an-inch or nore in thickness. With straps of suchdimensions, it is iecessary to perform them with the bends in the endshereof that are welded to the coil, as by heating the stock o a hightemperature and hammering it into the de- `ired shape.

Also as indicated, the practice heretofore has been o form the outerends of the straps with bends in them, he straps being of sufficientlength that the bend ends extend out of the furnace to points where theymay be connected to a current source. As explained, such a structurerequires that all the straps be led out of the furnace at one end of thecoil, so that the coil could be removed from that end of the furnace forreplacement.

However, with my invention it is possible to remove the coil from eitherend of the furnace lwhen it is necessary that it be replaced. To thisend, the ends of the straps extending past the opposite ends of the coil26 are not formed with any bends therein, but there is welded to theouter end of each strap 31-34 a stack of a plurality of elongated metalAlea-ves 31"-34. With reference to FIGURE 7, the edges of the stack ofleaves 31 are welded together at one end and to the one surface of theend of the strap 31, as indicated at 35. Preferably, these elements arewelded together so that the welds 35 are formed of parent metal, such asby the heliarc welding technique.

After the metal straps 31-34 are welded to the heating coil 26, and thestacks of metal leaves 31'-34' are welded to the outer ends of the metalstraps 31-34, the sections of the refractory tube 25 are placed aroundthe coil and insertedl in a surrounding tube 37 of refractory material.

The tube 37 is substantially coextensive with the tube 25,

and is supported within the housing 16 by surrounding bands 38-40 ofheat insulation (eg. rock wool or the like) and refractory materials.The annular spaces between the ends of the bands 38-40 and the innerwalls of the caps 21, 22 are lled with rings 41 of suitable refractorymaterial.

After sliding the assembly of the refractory tube and heating coil 26inside the tube 37, the stacks of metal leaves 31'-34' are led out ofthe opposite ends of the housing 16 and clamped to electrical terminalIblocks 44. Referring to FIGURES 5 and 6 along with FIGURES l and 2, therespective slots 45 for each of the stacks of leaves 31'-34 are formedin the end caps 21, 22 of the housing 16, each slot 45 extendingoutwardly from the central openings 23, 24. Additionally, the pair ofslots 45 in each end of the housing are located in the forward portionsof those ends, i.e., nearest the front of the cabinet module. In thisconnection, it Will be observed that the straps at each end are weldedto portions of the coil that are angularly displaced. Accordingly, theslots `45 are similarly displaced in the ends of the housing.

Referring to FIGURES 2, 5 and 6, each terminal block 44 is formed of arigid rectangular block 50 of electrical insulation which on its lowersurface is provided with a downwardly extending projection 50 extendingpart way along its length of one end thereof, and which is adapted to beinserted'in the slot 45. The block 50 has a rectangular opening 51 whichextends through the bottom projection 50. Additionally, the block 50 isprovided with a pair of upwardly projecting threaded bolts 52, the headsof which (see FIGURE `6) are located in countersunk openings ofsufficient size that the lower surfaces of the heads are above the planeof the lower surface of the block. The bolts 52 may be embedded in theblock or, as indicated, secured in place by nuts 53 threaded thereon totightly engage the upper surface of the block.

As shown, the block 50 is kept out of contact with the surface of theend cap 21 by a strip 54 of heat insulation, which may be made ofasbestos or the like. The insulation strip 54' is a rectangular elementof the outer dimensions of the block 50 having a slot 54 therein of thedimensions of the slot 45. The block 50 is secured to the end cap 21,with the insulation strip 54 sandwiched therebetween, in any suitablemanner, e.g., as by nut and bolt connections 55.

Preparatory to securing the block 50 in place, the stack of metal leavesare threaded through the slot 45 and the opening 51 in the block 50.Thereafter, the block is lowered along the leaves to be seated againstthe outer surface of the end cap 21 and secured in place. Referring toFIG- URE 6, the grouped metal leaves 31 are then bent and placed overthe upper surface of a conductor plate 58 which is supported at one endon the threaded ends of the bolts 52, such bolts extending throughopenings 59 (see FIGURE in the plate. Then a metal strip 60 havingopenings `61 aligned with the bolts 52 is lowered onto the bolts againstthe outer leaf of the stack 31', and nuts 62 are threaded onto the upperends of the bolts 52 and tightened securely to compress the leaves intofirm faceto-face contact with each other and insure firm face-tofacecontact between the bottom leaf of the stack and the upper surface ofthe conductor plate 58.

With the terminal blocks 44 secured to the ends of the housing 16, thecartridge unit 15 is ready for mounting in the cabinet module 12. It isplaced in the tray 17, which has been pulled forward to the exterior ofthe cabinet, and with the terminal blocks 44 located in the forwardpositions as shown in FIGURE 1. Before the tray 17 is shoved inwardly,electrical connections within the base cabinet portion 11 are connectedto the terminal blocks 44. To this end, and referring to FIGURES 2 and6, each conductor plate 58 extends past the outer end of the insulationblock `50, and is provided with an opening 63 to receive the threadedend of a bolt 64 on which the lug 65 of an insulated conductor 66 isplaced. A nut and washer combination 67, 68 are placed over the upperend of the threaded bolt `64, and the nut turned on the bolt until thelug y65 is securely clamped to the conductor plate 58.

After the conductors 66 are connected to the terminal blocks 44, thetray 17 is moved inwardly to position the capsule 15 inside the cabinetmodule 12. When this is done, the openings 23, '24 in the ends of thehousing 16 are brought into alignment with enlarged openings 70 in theends of the cabinet. Referring to FIGURE 2, along with FIGURE l, an endplug 71 of refractory materials is inserted in the opening 70. The outerdiameter of the plug 71 is only slightly less than the diameter of theopening 24 in the end cap 22, so that it can readily pass through thatopening. The plug 71 at its inner end has a reduced diameter, indicatedat 72, and at its inner end the plug abuts the end of the refractorytube 25 in which the heating coil 26 is located. As shown, the plug 71is notched at its inner end, as indicated at 73, to provide a passa-gefor the stack of metal leaves 34', to facilitate leading the stack ofleaves to the exterior of the housing with a minimum of bending.

After the plug 71 is inserted in each end of the housing, a sealing ring74 of suitable heat insulation material such as asbestos rope, is placedaround the axial lip or flange 75 which defines the end opening 24 ofthe housing 16. Thereupon, a short cylindrical element 77 is inserted inthe opening 70 of the cabinet 13, such element 77 having an externalflange 78 which fits against the outer surface of the cabine 13. Theinner end of the element 77 is curved or ared slightly, and engages thesealing ring 74. The ange 78 is secured to the wall of the cabinet 13,as by means of a trim plate 81 placed around the flange, and with nutand bolt connections I82, 83 for clamping the flange 78 between theplate 81 and the wall of the cabinet 13. Thus clamped, the inner end 79of the cylindrical element 77 firmly engages the sealing ring 74 andpresses it against the end cap 22. Thereafter, the front panel 14 issecured in place.

With the furnace capsule 15 thus completed, it is ready for use. In suchuse, a conventional quartz tube 85 (see FIGURE 2) is extended throughthe cabinet from end to end. The ends of the quartz tube 85 aresupported by the refractory plugs 71 and the outside trim plates 81,such elements for this purpose being provided with internal openings toslidably receive the quartz tube.

With the aobve-dcscribed arrangement for clamping the ends of thehousing 16 in place, the cartridge 15 cannot readily be dislodged fromoperating positions, as upon opening the front panel and inadvertentlypulling on the tray 17. Before the tray can be pulled out, and pull thecartridge 15 with it, the end clamping elements 77 have to be removed,along with the end refractory plugs 71. Also, of course, the quartz tubemust be removed. However, the operations for removing these elements canbe seen to be easy to accomplish, and can be done in a minimum of timewhen it is desired to service or replace the cartridge 15.

To remove the heating element itself, it is necessary only to remove theouter trim plates 81, the clamping cylinder 77 and the refarctory plug71 as above described, and to pull the tray 17 out. The conductors 66are then removed from the conductor plates 58, and the stacks of leaves31-34 are unclamped from the conductor plates. Since the leaves of thestack 31-34 are relatively thin members, being formed of, for example,elements of the order of .G25-inch thickness, they can readily be bentinwardly to clear the opening in the supporting refractory tube 37.Since the interior of the supporting tube 37 is equal to the outerdiameter coil-supporting tube 2S and the thickness of one of the straps33, 34, the unit assembly of the heating coil with its straps andsupporting tube 25 is easily slidable in the support tube 37, and caneasily be pulled out of either end of the support tube 37.

After removal of the heating unit as above described, a replacement unitof the same construction can be slidably inserted in the support tube37. In this connection, it will be understood that the entire terminalblock assemblies 44 are removed in order -to facilitate bending thestacks of leaves 3134' inwardly as described for easy removal of theheating unit. When a new -unit is positioned in the support tube 37, thestacks of leaves welded to the metal straps thereof are forced outwardlythrough the slots 45, and the terminal blocks assembled as in the mannerpreviously described.

The above-described operations for replacing the heating unit While thehousing 16 remains in the tray 17 may not be permitted in an area wherethe dust from the refractory material cannot be allowed to enter thesurrounding air. In thatlcase, since the housing 16 merely sets in thetray 17, the entire cartridge 15 can be lifted out of the tray andremoved from the area while the heating unit is being replaced.

Still further, if production operations must be continued while aheating unit is being replaced, it is a simple matter to lift the entirecartridge unit 15 from the tray 17, replace it with another completecartridge, making the necessary connections for the conductors, andquickly installing the new cartridge in place. Then the cartridge thathas been replaced can be taken out of the area and its heating unitreplaced, whereby it is available as a standby cartridge for usewhenever it is needed.

From the foregoing, it will be apparent that modifications can be madein various parts of the invention illustrated and described hereinwithout departing from its spirit and scope. Accordingly, I do notintend that my invention be limited, except as by the appended claims.

I claim:

1. Furnace apparatus comprising:

an elongated housing having end walls with central openings therein;

a body of refractory material supported in said housing and having acylindrical opening aligned with said central openings; Y

an elongated heating coil extending through the opening in said body;

a respective rigid metal strap Welded to each end of said coil, saidstraps extending parallel to said axis;

a respective stack of elongated metal leaves welded at one end to theouter end of each strap, said stacks at their opposite ends extendingthrough the central openings in said end walls, the outer ends of saidstacks being bent outwardly, said outer ends being bendable inwardly topermit said coil to be removed through either end of said body andhousing;

and respective electrical terminal means insulatingly and releasablysupporting said outer end of said stacks against said end walls.

2. 'Furnace apparatus as defined in claim 1 including tap connections toturns of the coil inwardly of the ends thereof, said connections beingformed of rigid metal straps extending parallel to said coil past theopposite ends thereof;

a pair of elongated stacks of metal leaves each welded at one end to theouter end of one of the last-mentioned metal straps, said metal leavesbeing bent outwardly and bendable inwardly in the same manner as thefirst-mentioned stacks;

and respective electrical terminal means insulatingly and releasablysupporting the outer ends of said lastmentioned stacks against said endwalls.

Furnace apparatus as defined in claim 2, including tube of refractorymaterial within the cylindrical opening in said body, said tubeenclosing said coil, said tube being formed of s emicylindricalsections, said straps forming the tap connections extending along theouter surface of said tube, the inner ends of such straps being bentinwardly and extending through said tube.

Furnace apparatus as defined in claim 3, including a plug of refractorymaterial filling the opening in each end wall of said housing andabutting the adjacent end of said tube, said plugs having centralopenings to slidably receive and support the ends of a quartz tubeextending through the center of said coil.

5. Furnace apparatus as defined in claim 4, including a cabinet havingend walls with openings therein and spaced from the end walls of saidhousing, said plugs extending substantially to the end walls of saidcabinet;

and means for releasably clamping said housing between the end walls ofsaid cabinet.

6. Furnace apparatus as defined in claim 5, including a tray in thebottom of said cabinet and slidable to the exterior thereof, and saidhousing being supported in said tray.

7. In combination:

an elongated heating coil;

a pair of axially directed, rigid metal straps welded to the ends of thecoil;

additional rigid metal straps welded to the turns of the coilintermediate the ends thereof, each of said additional straps extendingin opposite directions along said coil and past the ends thereof;

and a respective stack of elongated metal leaves welded together at oneend and to the outer end of each metal strap.

8. The combination defined in claim 7,

said additional straps being pre-formed with bends in the end thereofthat are welded to the coil turns, whereby such straps are spaced fromsaid coil;

and a tube of refractory material surrounding said coil,

said additional straps extending along the outer Surface of said tube,the bent ends of said straps extending through the Wall of said tube.

9. A furnace structure comprising:

a base cabinet housing electric controls for respective furnace heatingunits;

cabinet modules for each unit stacked on said base cabinet, each modulebeing formed as a box having a removable front panel;

:an elongated capsule enclosing a heating unit having a heating coil;

a drawer mechanism mounted at the floor of each module and having aslidable tray carrying a respective capsule, said tray being slidable toa close-d position in which said capsule thereon is inside its module,said tray being slidable to an open position in which, when the frontpanel is removed, the capsule thereon is held exteriorly of its module;

Aelectrical connecting means for each coil extending from the basecabinet to each module;

means carried by each capsule for releasably connecting selected pointson each coil to be associated electrical connecting means;

and means for releasably holding each capsule in its module in theclosed position of its tray.

10. A furnace structure as defined in claim 9,

wherein each capsule has openings at the ends thereof,

wherein said releasable connecting means includes respective stacks ofleaf conductor strips welded at one end to a respective rigid metalstrap, each strap being welded to a selected point on its associatedcoil,

the outer end of each stack extending through the opening in its capsulenearest the point of the coil to which it is conductively connected;

and a respective terminal means for releasably and insulatingly holdingthe outer end of each stack to the adjacent end of the capsule, and forconductively connecting a respective electrical connecting means to thestack.

11. A diffusion furnace comprising a base unit, a cabinet unit and atleast one cartridge heating assembly, electric control means for saidcartridge heating assembly housed in said base unit, said cabinet unitremovably housing said cartridge heating assembly, said cartridgeheating assembly comprising an elongated heating coil, insulatingmaterial, and an elongated outer shell, said insulating material beinginterposed between said heating coil and said shell, said cabinet unithaving end members generally perpendicular to the axis of said elongatedheating coil, at least one of said end members permitting access to theinterior of said elongated heating coil and exposable supporting meanswithin said cabinet unit releasably supporting said cartridge heatingassembly whereby when said assembly is exposed from said cabinet unit,said assembly can be readily removed from said supporting means.

12. A diffusion furnace as in claim 11 wherein a plurality of saidcartridge heating assemblies are horizontally disposed in a vetricallystacked relationship in said cabinet unit.

13. A diuson furnace as in claim 11 wherein said supporting means forsaid cartridge heating assembly comprises a member slidably supported bysaid end members.

14. A diffusion furnace as in claim 11 wherein said cabinet unit has aback wall and a front wall, said front wall being at least in partremovable to permit said cartridge heating assembly to be exposed.

15. A diffusion furnace as in claim 11 wherein a support tube formed ofrefractory material is interposed between said shell and said heatingcoil, said support tube and said heating coil being disposed in coaxialrelationship.

16. A diusion furnace wherein the support tube defined in claim 15 hasan interior groove to nestably receive thte outer portions of saidelongated heating coil.

17. A diffusion furnace as in claim 14 wherein said supporting means isa drawer member slidably supported by said end members.

References Cited The following references, cited by the Examiner, are

of record in the patented file of this patent or the original patent.

UNITED STATES PATENTS 1,282,330 10/1918 Van Aller 219-390 y1,588,5566/1926 Thompson 339-9 1,930,836 10/1933 DAmico 219-390 2,527,026 10/1950 Mucher 338-323 2,535,379 12/1950 White 219-403X 3,178,665 4/1965Matheson et al 338-299 3,299,196 l/1967 Lasch et al 13-24 FOREIGNPATENTS 877,776 9/ 1961 Great Britain 219-541 930,298 8/1947- France13-25 VOLODYMYR Y. kMAYEWSKY, Primary Examiner

